H: H-Hz | Newton[ap]s Telecom Dictionary

H-Hardware Tree

H

The symbol designation for magnetic inductance.

H PAD

Host Packet Assembler/Dissembler. See HPAD.

H Schedule

A separate and distinct list in the translations area of program store in No. 1 or 1A ESS central office. The H (hourly) Schedule is normally used for collecting counts on items required for day-to-day administration of the central office equipment and for the engineering of general growth jobs. They include such items as call processing registers, service circuits and miscellaneous trunks, intraoffice trunks and junctors networks.

H-1B Visa

A visa issued by the Immigration and Naturalization Service to skilled workers coming from overseas to work in American companies. Typically those visas are issued to to workers who have scarce skills.

H-Channel

The packet-switched channel on an ISDN PRI (Primary Rate Interface) which is designed to carry user bandwidth- intensive videoconferencing information streams at varying rates, depending on type: H0 ” 384 Kbps; H11 ” 1,536 Kbps; and H12 ” 1,920 Kbps. In short, H-channels are ISDN bearer services that have pre-defined speeds, starting and stopping at locations on an ISDN PRI circuit. They are contiguously transported from one ISDN PRI site through networks to another ISDN PRI site. H-channels are accomplished by aggregation of multiple individual 64Kbps B channels; in the carrier domain, this aggregation is accomplished through a process known as "bonding." See ISDN and PRI.

H-MVIP

The original MVIP standard, now called MVIP-90, was developed in 1989-90 and first deployed in 1990. MVIP-90 supports up to 512 telephony channels of 64 Kbps each between circuit boards within a single computer chassis. MVIP-90 has been widely adopted for voice, FAX, data and video services as well as for telephony switching applications. Other MVIP standards have since been developed to address multi-chassis MVIP systems and higher level software APIs. Beginning in 1993, there was interest in higher capacities within individual single-chassis MVIP nodes. Specific applications include large audio conferences, multi-media servers, and the termination and switching of all traffic on a dual FDDI-II fiber ring (as used in MC2 standard Multi-Chassis MVIP) as well as the termination of and switching of traffic from T-3/E-3 telephone trunks and SONET/SDH links at OC-3 (155 Mbps) rates (as used in MC3 standard Multi-Chassis MVIP). H-MVIP addresses this need for higher telephony traffic capacity in individual computer chassis.

H-MVIP defines three major items that together make a useful digital telephony transport and switching environment. These are the H-MVIP digital telephony bus with up to 3072 "time-slots" of 64 Kbps each; a bus interface with digital switching that allows a group of H-MVIP interfaced circuit boards to provide distributed telephony switching and a logical device driver model and standard software interface to that logical model. The bus definition includes the mechanical, electrical and timing requirements for a high capacity telephony bus that is a super-set of the existing MVIP-90 standard for computer-based telephony. Several levels of capacity expansion are defined to support a range of system implementations . Among them, H-MVIP "24/2" is a wider version of MVIP-90, while the full H-MVIP bus is both wider and faster. See ECTF, SCSA and TAO.

H.100

H.100 is a hardware specification that provides all the necessary information to implement a CT Bus interface at the physical layer for the PCI computer chassis card slot independent of software applications. It is the first card-level definition of the overall CT Bus single-communications bus specification. CT Bus defines a single isochronous communications bus, often called a mezzanine bus, across newer PC chassis card slots (PCI, and the emerging compact PCI). H.100 CT Bus will be compatible with the most popular existing implementations, SCBus, HMVIP and MVIP (as well as ANSI VITA 6) implemented in ISA/EISA card slots. A CT Bus specification for compact PCI, H.110, is also under development for a later release.

Adoption of the single-bus specification, CT Bus, will allow a fluid inter-operation of components to provide an unprecedented level of flexibility for product design and operation. CT Bus provides more capacity to allow development of a new class of applications as well as to increase the capabilities of existing applications. Its addition of greater fault-tolerance will increase the reliability of applications, and its provision for implementing a subset of the specification will provide for many lower cost applications. H.100 offers the following features:

A PCI card slot form factor to accommodate the growing popularity of PCI slots in computer chassis.
4,096 bi-directional time slots (permitting up to 2,048 full duplex calls) for larger communications capacity.
An eight megabit data rate and 128 channels per stream for greater bandwidth.
Redundant clocking scheme for increased fault tolerance.
Backwards compatibility and interoperability with SCBus, HMVIP and MVIP.

The H.100 is part of a complementary suite of Interoperability Agreements sponsored by the ECTF (Enterprise Computer Telephony Forum). Each specification is fully self contained, yet designed to be complementary with all of the others in the suite. Other ratified specifications include S.100 and S.200. Software developers are creating applications with the S.100 and S.200 specifications, and hardware manufacturers will introduce H.100- based communications cards.

S.100, published in March, 1996 specifies a set of software interfaces that provide an effective way to develop CT applications in an open environment, independent of underlying hardware. It defines a client-server model in which applications use a collection of services to allocate, configure and operate hardware resources. S.100 enables multiple vendors ' applications to operate on any S.100-compliant platform.

H.110

H.110 defines H.100 on the CompactPCI (cPCI) Bus. The biggest difference between H.100 and H.110 is that H.110 supports CompactPCI Hot Swap (the removal and insertion of cards in a live system). www.ectf.org/ectf/home.html. See also H.100.

H.221

A framing recommendation which is part of the ITU-T's H.320 family of video interoperability recommendations. The recommendation specifies synchronous operation where the coder and decoder handshake and agree upon timing. Synchronization is arranged for individual B channels or bonded 384 Kbps (HO) connections.

H.222.0

Defines the general form of elementary stream multiplexing as the Moving Picture Experts Group 2 (MPEG-2) system part. See H.222.1.

H.222.1

Specifies the parameters of H.222.0 for communication use.

H.225.0

This is H.323 protocol based on RAS and ISDN's Q.931. It is used for establishing calls.

H.230

A multiplexing recommendation which is part of the ITU-T's H.320 family of video interoperability recommendations. The recommendation specifies how individual frames of audiovisual information are to be multiplexed onto a digital channel.

H.231

A recommendation, formally added to the ITU-T's H.320 family of recommendations in March, 1993, which specifies the multipoint control unit used to bridge three or more H.320-compliant codecs together in a multipoint conference.

H.233

A recommendation, part of the ITU-T's H.320 family, which specifies the encryption method to be used for protecting the confidentiality of video data in H.320-compliant exchanges. Also called H.KEY.

H.234

ITU-T standard for delivering encryption key management and authentication system for audiovisual services.

H.235

An ITU-T standard (February, 1998) for securing H.323 voice and videoconference information streams over IP networks (e.g., the Internet, Intranets and LANs). H.235 provides authentication, integrity and privacy services. Authentication serves to establish as genuine the identity of all endpoints in the conference in order that unauthorized users or machines cannot participate. Integrity validates the payload of data packets, thereby ensuring that the data was neither corrupted nor altered in transit. Privacy, accomplished through an encryption mechanism, ensures that the data payload cannot be read by users or machines not authorized. Non- repudiation , planned for inclusion in future releases of H.235, protects against an endpoint's denial of participation in the conference. See also H.323.

H.242

Part of the ITU-T's H.320 family of video interoperability recommendations. This recommendation specifies the protocol for establishing an audio session and taking it down after the communication has terminated .

H.244

Recommendation on a channel aggregation method for audiovisual communications. This enables several ISDN B-channels to behave as a single higher-rate channel.

H.245

H.245 specifies the signaling protocol necessary to actually establish a call, determine capabilities, and issue the commands necessary to open and close the media channels. The H.245 control channel is responsible for control messages governing operation of the H.323 terminal, including capability exchanges, commands, and indications .

H.245 does not use in- band signaling, but uses data packets sent a data network. See H.323 and TAPI 3.0.

H.245

H.245 specifies a control protocol for multimedia communication. It is responsible for establishing informational channel for voice packets exchange between two terminals just after the call is established. H.245 specifies which IP-addresses are to be used for transport, which codecs are supported by terminals and so on. It also includes some messages for MCU control.

H.246

See H.245.

H.248

The ITU-T recommendation for MGCP (Media Gateway Control Protocol), which is an open, standards-based signaling and control protocol for use between circuit-switched PSTNs (Public Switched Telephone Networks) and VoIP (Voice over Internet Protocol) networks. H.248 is compliant with Signaling System R2, which is an international signaling system within international regions , for integrating international/national signaling. See also MGCP and R2.

H.261

The ITU-T's H.261 is the standards watershed in videoconferencing. Also known as p x 64, H.261 specifies the video coding algorithms, the picture format, and forward error correction techniques to make it possible for video codecs from different manufacturers to successfully communicate. H.261 is an ITU-standard video codec designed to transmit compressed video at a rate of 64 Kbps and at a resolution of 176 x 44 pixels (QCIF). Announced in November 1990, it relates to the decoding process used when decompressing video conferencing pictures, providing a uniform process for codecs to read the incoming signals. Any H.323 client is guaranteed to support the following standards: H.261 and G.711. Other important standards are H.221: communications framing; H.230 control and indication signals and H.242d: call set-up and disconnect. Encryption, still-frame graphics coding and data transmission standards are still being developed. See H.320.

H.263

H.263 is an ITU-standard video compression protocol that improves video streaming over a corporation's LAN or WAN. It is based on and compatible with H.261. It offers improved compression over H.261 and transmits video at a resolution of 176 x 44 pixels (QCIF).

H.310

Recommendations for a videoconferencing terminal in an ATM environment.

H.320

The most common family of ITU-T videoconferencing standards. These standards allow ISDN BRI videoconferencing systems and videophones to communicate with each other. I've personally had several H.320 compatible videoconferencing systems and video- phones on my desk and have received from and made videoconferencing calls to many different H.320 compatible video phones. The quality is not brilliant . But you can recognize the person at the other end. And they can recognize you. Most H.320 systems allow you to bond together the two B channels of a 2B+D ISDN BRI channel and thus get better video. See all the H.2NN and H.3NN explanations above and below. See also G.711 and V.80.

H.321

The adaptation to the ATM environment of H.320 videoconferencing standards. See H.320 and V.80.

H.322

The adaption to a guaranteed quality of service LAN of H.320 terminals. See H.320 and V.80.

H.323

H.323, a standard from the International Telecommunications Union (ITU-T), which serves as the "umbrella" for a set of standards defining real-time multimedia communications for packet-based networks ” what are now called IP telephony. Much of the excitement surrounding the H.323 standards involves the use of H.323 entities to communicate over the Internet or privately-managed and privately-owned Internet Protocol (IP) networks. The standards under the H.323 umbrella define how components that are built in compliance with H.323 can set up calls, exchange compressed audio and/or video, participate in conferences, and interoperate with non-H.323 endpoints.

H.323 is an ITU-T standard, which defines a set of call control, channel setup and codec specifications for transmitting real-time voice and video over networks that don't offer guaranteed service or quality of service ” such as packet networks, and in particular Internet, LANs, WANs and Intranets. This ITU-T standard (ratified initially in March of 1996) defines the negotiation and adaptation layer for video and audio over packet switched networks. "Negotiation" means that this layer defines the way the devices on either end of the data conversation will figure out what is the fastest speed they can accommodate. H.323 does- n't mean you get good videoconferencing over lousy circuits. But it does mean that you should get some videoconferencing. H.323 is comprised of the following standards:

H.225: Middleware which specifies a message set for call signaling registration and admissions, supporting call negotiations ” i.e. synchronization.
H.245: Adds the ability to open and close logical channels on the network, i.e. transmission control.
G.711: Pulse Code Modulation (PCM) (64 Kbps) encoder/decoder specification for voice.
G.722: 7 kHz audio-coding.
G.723.1: Speech encoding/decoding with a low bit rate, high output quality. This is the default encoder required for H.323 compliance.
G.728: Encoding/decoding of speech at 16 kbps using low-delay code excited linear predictive methods .
G.729: Encoding/decoding of speech at 8 kbps using conjugate-structure, algebraic-code excited linear predictive methods.

The H.323 standard has the endorsement of several key client vendors such as Netscape, for use within their Cool Talk application; Microsoft, for use in NetMeeting, now part of Internet Explorer; and Intel, for their Internet Phone product. With Netscape and Microsoft representing approximately 95% of the Internet browser market, and Intel and Microsoft dominating the current platforms, this collective support makes H.323 a defacto standard. See H.320, H.324 and V.80.

In September, 1997, Microsoft issued a white paper on "IP Telephony with TAPI." In that paper, Microsoft said:

H.323 is a comprehensive International Telecommunications Union (ITU) standard for multimedia communications (voice, video, and data) over connectionless networks that do not provide a guaranteed quality of service, such as IP-based networks and the Internet. It provides for call control, multimedia management, and bandwidth management for point- to-point and multipoint conferences. H.323 mandates support for standard audio and video codecs and supports data sharing via the T.120 standard. Furthermore, the H.323 standard is network, platform and application independent, allowing any H.323 compliant terminal to interoperate with any other. H.323 allows multimedia streaming over current packet-switched networks. To counter the effects of LAN latency, H.323 uses as a transport the Real-time Transport Protocol (RTP), an IETF standard designed to handle the requirements of streaming real-time audio and video over the Internet.

H.245 for call control
Q.931 for call signaling
The RAS (Registration, Admissions, and Status) signaling function The H.245 control channel is responsible for control messages governing operation of the H.323 terminal, including capability exchanges, commands, and indications. Q.931 is used to set up a connection between two terminals, while RAS governs registration, admission, and bandwidth functions between endpoints and gatekeepers (RAS is not used if a gatekeeper is not present). See below for more information on gatekeepers.

H.323 defines four major components for an H.323-based communications system:

Terminals
Gateways
Gatekeepers
Multipoint Control Units (MCUs)

Terminals are the client endpoints on the network. All terminals must support voice communications; video and data support is optional. A Gateway is an optional element in an H.323 conference. Gateways bridge H.323 conferences to other networks, communications protocols, and multimedia formats. Gateways are not required if connections to other networks or non-H.323 compliant terminals are not needed. Gatekeepers perform two important functions which help maintain the robustness of the network - address translation and bandwidth management. Gatekeepers map LAN aliases to IP addresses and provide address lookups when needed. Gatekeepers also exercise call control functions to limit the number of H.323 connections, and the total bandwidth used by these connections, in an H.323 "zone." A Gatekeeper is not required in an H.323 system-however, if a Gatekeeper is present, terminals must make use of its services.

H.323 Components: Multipoint Control Units (MCU) support conferences between three or more endpoints. An MCU consists of a required Multipoint Controller (MC) and zero or more Multipoint Processors (MPs). The MC performs H.245 negotiations between all terminals to determine common audio and video processing capabilities, while the Multipoint Processor (MP) routes audio, video, and data streams between terminal endpoints. Any H.323 client is guaranteed to support the following standards: H.261 and G.711. H.261 is an ITU-standard video codec designed to transmit compressed video at a rate of 64 Kbps and at a resolution of 176x44 pixels (QCIF). G.711 is an ITU-standard audio codec designed to transmit A-law and -law PCM audio at bit rates of 48, 56, and 64 Kbps. Optionally, an H.323 client may support additional codecs: H.263 and G.723. H.263 is an ITU-standard video codec based on and compatible with H.261. It offers improved compression over H.261 and transmits video at a resolution of 176 x 44 pixels (QCIF). G.723 is an ITU-standard audio codec designed to operate at very low bit rates. The TAPI 3.0 H.323 Telephony Service Provider The H.323 Telephony Service Provider (along with its associated Media Stream Provider) allows TAPI-enabled applications to engage in multimedia sessions with any H.323-compliant terminal on the local area network. Specifically, the H.323 Telephony Service Provider (TSP) implements the H.323 signaling stack. The TSP accepts a number of different address formats, including name, machine name , and e-mail address. The H.323 MSP is responsible for constructing the DirectShow filter graph for an H.323 connection (including the RTP, RTP payload handler, codec, sink, and renderer filters).

H.323 telephony is complicated by the reality that a user's network address (in this case, a user's IP address) is highly volatile and cannot be counted on to remain unchanged between H.323 sessions. The TAPI H.323 TSP uses the services of the Windows NT Active Directory to perform user-to-IP address resolution. Specifically, user-to-IP mapping information is stored and continually refreshed using the Internet Locator Service (ILS) Dynamic Directory, a real-time server component of the Active Directory. See TAPI 3.0.

The official ITU definition of H.323 is as follows : H.323 describes terminals, equipment and services for multimedia communication over Local Area Networks (LAN) which do not provide a guaranteed quality of service. H.323 terminals and equipment may carry real- time voice, data and video, or any combination, including videotelephony.The LAN over which H.323 terminals communicate, may be a single segment or ring, or it may be multiple segments with complex topologies. It should be noted that operation of H.323 terminals over the multiple LAN segments (including the Internet) may result in poor performance. The possible means by which quality of service might be assured on such types of LANs/internetworks is beyond the scope of this Recommendation.H.323 terminals may be integrated into personal computers or implemented in stand-alone devices such as videotelephones. Support for voice is mandatory, while data and video are optional, but if supported, the ability to use a specified common mode of operation is required, so that all terminals supporting that media type can interwork. This Recommendation allows more than one channel of each type to be in use. Other Recommendations in the H.323-Series include H.225.0 packet and synchronization, H.245 control, H.261 and H.263 video codecs, G.711, G.722, G.728, G.729, and G.723 audio codecs, and the T.120-Series of multimedia communications protocols.This Recommendation makes use of the logical channel signalling procedures of Recommendation H.245, in which the content of each logical channel is described when the channel is opened. Procedures are provided for expression of receiver and transmitter capabilities, so transmissions are limited to what receivers can decode, and so that receivers may request a particular desired mode from transmitters. Since the procedures of Recommendation H.245 are also used by Recommendation H.310 for ATM networks, Recommendation H.324 for GSTN, and V.70, interworking with these systems should not require H.242 to H.245 translation as would be the case for H.320 systems.H.323 terminals may be used in multipoint configurations, and may interwork with H.310 terminals on B-ISDN, H.320 terminals on N-ISDN, H.321 terminals on B-ISDN, H.322 terminals on Guaranteed Quality of Service LANs, H.324 terminals on GSTN and wireless networks, and V.70 terminals on GSTN. See TAPI 3.0.

H.324

Standard for analog POTS telephone line based videoconferencing via modems.

H.324 is an interoperability standard, meaning that if a vendor's videoconferencing product conforms to H.324 it should communicate with all the other vendors who say their products conform to H.324. H.324 contains several standards for videoconferencing. They are H.263 for real time video compression/decompression. G.723 for real time audio compression/ decompression , H245/H.223 control protocol and multiplexing and V.80 application interface for modems. See H.320 and V.80.

H.450

Supplementary services for H.323 (since 2nd version).

H.gcp

A proposed new ITU-T standard being added to the H.323 family of ITU-T recommendations, which have been widely adopted by industry as the main standards for multimedia communications over the Internet. H.gcp will permit control of gateway devices that pass voice, video, facsimile and data traffic between conventional telephony networks, i.e. the Public Switched Telephone Network and packet based data networks such as the Internet. Connections through such gateway devices allow callers from a normal telephone to make long distance voice calls over the Internet. According to the ITU-T, the H.323 family of standards already provides an extensive framework for the provision of new services. The new recommendation (i.e. H.gcp) will permit low-cost Internet gateway devices for the first time to be interfaced in a standard way with the signaling systems found in conventional telephony networks.

H.R.nnnn

A proposed law introduced into the House of Representatives by a Congressman. Typically, four digits follow the H.R., signifying the proposed bill's number. The reason for including this definition in this dictionary is that every few months since divestiture some Congressman has attempted to introduce a bill into the House of Representatives changing the Communications Act of 1934. Such a bill is generally supported by a bevy of Bell telephone companies trying to use the proposed bill to remove those restrictions placed on them by Divestiture ” manufacturing, creating information content and getting into long distance.

H0 Channel

An H zero channel is a 384 kbps channel that consists of six contiguous DS0s (64 kbps) of a T-1 line.

H10 Channel

The H ten channel is the North American 1,472 Kbps channel from a T-1 or primary rate carrier. It is equivalent to twenty-three (23) 64 kbps channels.

H11 Channel

The North American primary rate used as a single 1,536 Kbps channel. This channel uses 24 contiguous DS0s (DS zeros) or the entire T-1 line except for the 8 Kbps framing pattern.

H12

The European primary rate used as a single 1,920 kbps channel (30 64 kbps channels) or the entire E-1 line except for the 64 kbps framing and maintenance channel.

HA

Horn Alert. A cellular car phone feature that automatically blows the car's horn if a call is coming in.
Home Automation. See Home Automation.

HA Linux

High Availability Linux. The idea of HA linux project is to provide a high- availability (clustering) solution for Linux which promotes reliability, availability, and serviceability. The basic functions required by any HA system include starting and stopping resources, monitoring the availability of the systems in the cluster, and transferring ownership of a shared IP address between nodes in the cluster.

Hack

The output of a hacker. Usually good programs, but sometimes just something clever of no discernible use. Just a "good hack", or something done for the "hack value."

Hackademy

A school ” recently opened in Paris and now under police surveillance ” that teaches students how to break into computer systems.

Hacker

Originally, a person who "hacks" away at a programmable system (i.e., computer system and applications software) until it works. In contemporary lingo, a person who breaks into computer systems, usually over the Internet. The word hacker has gone through many meanings. In the late 1950s MIT students who loved to tinker with the university's gigantic early computers started calling themselves "hackers." At one stage being a hacker was a badge of honor conferred on an elite programmer or computer hardware designer. But in 1983 the movie "War Games" presented another view of the hacker mentality ” someone who tries to break into computer systems for fun and sport. Today the term tends to have positive meanings, while the word "cracker" is reserved for individuals who willfully break into computer systems seeking to wreak damage. See also Cracker, Hacker Ethic , Hacker Tourism, Phreak, Script Kiddies, and Sneaker.

Hacker Ethic

A set of moral principles common to the first generation hacker community. According to hacker ethic, all technical information should, in principle, be freely available to all. However, destroying, altering, or moving data in a way that could cause injury or expense to others is always unethical.

Hacker Tourism

From Wired's Jargon Watch column. Travel to exotic locations in search of sights and sensations that only a technogeek could love. The term was coined by Neal Stephenson in his colossal article for Wired on FLAG, a fiber- optic cable now being built from England to Japan.

Hailstorm

See Cloud, definition 2.

Hairpinning

Also known as tromboning in some applications, hairpinning is a term for data going into a network element (NE), making a hairpin turn , and going right back out. The term is fairly descriptive, if you visualize a hairpin and its u-shaped bend. Let's consider some examples of hairpinning. Specifically, let's consider hairpinning in the context of SONET fiber optics rings and routers.

A SONET OC-192 backbone metropolitan ring in Manhattan (NY) running at 10 Gbps might support multiple tributary subtending (i.e., lower level) OC-48 rings running at 2.5 Gbps, with each subtending ring serving a smaller geographic area of Manhattan. Each of the subtending rings is connected to the metro ring by a device in the form of an integrated ADM/OCX (Add/Drop Multiplexer and Optical Cross-Connect), with perhaps one such device serving to interconnect all of the rings. Traffic originating on the West Side Manhattan ring and terminating on the West Side ring is presented to the ADM/OCX and is hairpinned right back to the West Side ring without ever riding over either the internal bus of either the ADM/OCX or the transmission facility of the metro ring. Similarly, traffic originating on one West Side ring and intended for another West Side ring ( assuming that there is more than one) can be hairpinned on a port-to-port basis. This low speed-to-low speed, port-to-port direct interconnection is a very commonsense approach that eliminates congestion on the metro ring. Expand this example to include metro rings connected over long-haul rings, and the advantage becomes even clearer and more compelling.

A VoIP (Voice over Internet Protocol) gateway router also can take advantage of hairpinning. Using the Manhattan example again, you are calling from your West Side apartment to another address on the West Side. To access your IP-based CLEC (Competitive Local Exchange Carrier), who also is your ISP (Internet Service Provider), you use an ILEC (Incumbent LEC) local loop that connects to the CLEC through a traditional PSTN (Public Switched Telephone Network) circuit-switched CO (Central Office). When your call hits the CLEC gateway, a router converts your voice call to an IP packet format, the router hairpins the call right back to the ILEC PSTN, without going through the process of conversion to packet format and reconversion to PCM (Pulse Code Modulation) format. There really is no point in going through the process, and congesting the gateway router in the process. See also ADN, CLEC, CO, Gateway, ILEC, IP, ISP, OXC, PCM, PSTN, Router, SONET, Subtend, Tromboning, and VoIP.

HAL

The computer from the movie 2001: A Space Odyssey. HAL is an acronym for "Heuristically programmed ALgorithmic computer." The one-letter-shift transposition to "IBM" (The I became H. The B became A. The M became L) was noted shortly after the film's release and was widely accepted as a subtle Kubrick/Clarke joke directed at the computer giant. Clarke himself has pointed out that when he named HAL, he didn't catch the one-letter-shift bit, and if he had, he would have changed the name. IBM had been a huge supporter of the film project, and he wouldn't have dreamed of poking fun at them, however subtly. (Incidentally, according to Clarke, the one intentional joke in the film was the scene where a knuckle-chewing Heywood Floyd read the instructions for the Zero-Gravity Toilet.)

Half T-1

It's exactly half a T-1, i.e., a Fractional T-1 providing 12 channels at 64 Kbps, or 768 Kbps. It's provisioned exactly the same way as a T-1. In reality, it is a T-1 with half the channels turned off. Priced at a little over half a T-1. See T-1 and T Carrier.

Half-Bridge

Apple Computer term for a device linking LANS over a low-speed link such as a telephone line or X.25 link. It is termed a half-bridge as one is required at each end of the link.

Half-Circuit

When you buy an international circuit ” say one from America to France, you typically pay two fees. You pay one to your American telecom carrier for half the distance and you pay one fee to the French carrier for the second half of the distance. Think of a satellite circuit. You'd pay one fee for the uplink from the U.S. to the satellite and one for downlink from the satellite to France. Those fees may be the same; then they may not be.

Half-duplex

A circuit designed for data transmission in both directions, but not at the same time. Telex is an example of a half duplex system, as is speaking on with most speakerphones. (The best speakerphones are full duplex. They're rare and expensive.)

Half-duplex M-ES

A cellular radio term. A Mobile End System (M-ES) that can either transmit or receive, but cannot do both simultaneously , for example, an M-ES that has a single transceiver (radio).

Half-duplex Transmission

A technique of operating a communications circuit so that each end can transmit or receive, but not simultaneously. Normal operation is alternate, one-way-at-a-time transmission. See Half Duplex.

Half-life

In science, the time it takes for half the radioactivity of a substance to disappear. Among techies, it is a gauge of an individual's usefulness . "He may have a short half-life here."

Half-repeater

A device which extends the distance a LAN can cover by joining two lengths of cable over another communication medium.

Half-tapping

The action of making an analog trunk appear in two places for simultaneous service. Half-tapping refers to the duplication of service on the customer side of the demarcation point and back-tapping is the description used by the telephone company when the duplicate service originates from their side of the demarcation point. Half-tapping is useful when new telephone equipment is being installed in the same location as the current equipment because the new system can be tested while the old system is still in use.

Half-tone

Any photomechanical printing surface or the impression therefrom in which detail and tone values are represented by a series of evenly spaced dots in varying size and shape, varying in direct proportion to the intensity of tones they represent.

Half- transponder

A method of transmitting two TV signals through a single transponder through the reduction of each TV signal's deviation and power level. Half- transponder TV carriers each operate typically 4 dB to 7 dB below single-carrier saturation power.

Half-wave Antenna

An antenna which is half as long as the wave being received.

Halo Effect, The

Websters defines a halo as a conventional, geometric shape, usually in the form of a disk, circle, ring or rayed structure representing a radiant light around or above the head of a divine or sacred personage. A company or person acquiring "the Halo Effect" suggests that the company is doing that most outside observers really view as "right." In short, the company or person is on a major roll.

HAM

HAM or HAM-radio. Home AMateur radio. A person who operates a HAM radio. www.ham.org and www.fcc.gov.

HAM Operator

A person who operates a HAM radio. See HAM.

Hammer

Don't try to drive a nail with this baby. A 64-bit core of a microprocessor is called the hammer.

Hamming Code

An code used in Forward Error Correction (FEC). Named after R.

W. Hamming of Bell Labs, the basic code has four information bits and three check bits per character. Extended Hamming Code involves a set of data viewed as a two-dimensional data block which, for example, might be 11 bits horizontal (wide) and 11 bits vertical (deep). Along both the horizontal and vertical planes in this example, "(16,11) Extended Hamming Code" takes 11 information bits, computes 5 parity bits, appends the parity bits to the information bits, and sends the entire data block across the transmission facility. In total, the result is a (256,121) code, as 16x16=256 and 11x11=121. (The number of information bits can be greater in the vertical plane. This would be advantageous if the size of the data blocks is large, as the level of overhead would be less, relative to the data bits to be transmitted.) The receiving (i.e., Forward) device re-computes the parity bits, and compares the resulting bit sequences to those sent along with the data. If the two sets of parity bits do not match exactly, there almost certainly was an error created as the data transited the network. If errors are detected , the receiving device almost always has enough information to isolate the error, and to correct it without the requirement for a retransmission. See also Forward Error Correction and SISO.

HAN

Home Area Network. A residential network for data communication and control based on the same concepts as a LAN, but using standard electrical wiring. For more detail, see CEBus.

Han Characters

Han characters are Chinese language symbols which are used to represent whole words or concepts in Chinese, Japanese and Korean. See Unicode.

Hand Off

See Handoff .

Hand-off

See Handoff.

Handhole

A buried box whose lid is even with the surface of the ground. It provides a space for splicing and terminating cables.

Handle

In the Windows 95 user interface, an interface added to the object that facilitates moving, sizing, reshaping, or other functions pertaining to an object.
In programming, a pointer to a pointer that is, a token that lets a program access a resource identified in another variable. See also object handle.
The name you use in an online computer service. It's typically not your own name. You adopt this name to give yourself anonymity for whatever reasons you find convenient . A handle is called a "Nom de ligne" in some circles.

Handled Call

A call center term. A call that is answered by an employee, as opposed to being blocked or abandoned .

Handoff

The process by which the Mobile Telephone Switching Office (MTSO) passes a cellular phone conversation from one cell to another. There are two forms of handoff: hard and soft. A hard handoff is performed on a "break and make" basis, requiring the connection to be broken in the original cell before it is made in the successor cell . Hard handoffs are required in cellular systems using FDMA (Frequency Division Multiple Access), such as the analog AMPS (Advanced Mobile Phone System), and those using TDMA (Time Division Multiple Access), such as GSM (Global System for Mobile Communications). As AMPS and GSM employ different frequencies in adjacent cells , hard handoffs are required ” you don't notice the difference in a voice conversation, as the process takes only 250 milliseconds or so, but data communications are affected very adversely. A soft handoff, on the other hand, employs a "make and break" handoff algorithm. Some PCS (Personal Communications Services) systems employ CDMA (Code Division Multiple Access), which does not require the use of different frequencies in adjacent cells. Those systems, therefore, take advantage of soft handoffs. If the mobile user is moving quickly through cell sites (e.g. traveling in a car), handoff becomes harder and the user may get dropped. See also AMPS, CDMA, FDMA, GSM, MTSO, PCS, and TDMA.
To connect a phone call or service from one telephone company to another. These usually occur in a place called co-location.
The process of transferring a subscriber call from one satellite to another.
An SCSA definition. The change of ownership of a Group (and therefore, typically, a call) from one session to another. For example, if a call center application discovers that a caller wishes to access a technical support audiotex database, it hands off the call to an application servicing that database.

Handover Word

The word in the GPS (Global Positioning System) message that contains synchronization information for the transfer of tracking from C/A to P code.

Handset

The part of a phone held in the hand to speak and listen, it contains a transmitter and receiver. In the old days, the transmitter was a carbon mike. Now it's mostly electronic. Some electronic mikes are awful . Some phone makers are going back to carbon mikes . There are two basic types of telephone handsets in North America: the G-style hand- set, which has round, screw-in ear and mouthpiece, and the new K-style handset, which has square ear and mouthpiece and has the two screws in the middle. I prefer the older G- style one. I think it's sturdier. It also has the advantage that you can unscrew it and quickly remove the transmitter ” very useful if you want someone to listen in on your conversation, but you don't want the other party to hear his breathing and coughing.

Handset Management

Imagine you have a phone attached to your computer through a telephony board inside your computer. Now imagine that you pick up the phone and dial a number. If the company knows you have dialed a number and knows which number you have dialed , that feature is called handset management. It is the ability of the computer to be aware of every button pushed on the phone. The advantage of this is obvious: You really want the PC to collect those digits, so it can, for example, add a price to each call and use them for monthly billing (lawyer, accountant , etc.). You also want to be able re-dial those numbers by simply clicking on the number one you want, hitting Enter and bingo, you're redialing that number, without having to key it in again. This term, hand- set management, has now been replaced by a more meaningful term which we're now calling "Telephone Set Management."

Handsfree

This a term with different meanings in the telephone business. It can mean that you have a telephone with a speakerphone and thus you are able to talk on it "handsfree," i.e. without your hands touching the handset, but you still must dial manually. In the car phone business, it means the same thing, i.e. the ability to use your phone without lifting or holding the handset to your ear, plus it may mean that your car phone has voice recognition and you can also dial handsfree by talking to your car phone, e.g. "Call mother." See also Handsfree Dialing.

Handsfree Answerback

This feature, when activated, automatically turns ON the microphone at a telephone receiving a call so that the person receiving the call can respond without lifting the receiver. Handsfree answerback is typically used on intercom calls.

Handsfree Dialing

A telephone feature which allows the user to place outside calls and listen to the progress of those calls without lifting the handset of his telephone. This feature is unbelievably useful when calling airlines which inevitably put you on "eternity hold." (We made that term up.)

Handsfree Monitoring

You can dial an outside call and hear the call's progress without having to lift your handset. Similar to hands-free dialing. With hands-free monitoring, you can only listen. To speak, you must pick up the handset. To be able to speak, you need a full speakerphone. Be careful of the distinction. Many people have been caught.

Handsfree Telephone

Could be another word for a speakerphone or for a phone that does hands-free dialing.

Handshake

Two modems trying to connect. Two modems trying to agree on how to transfer data. The series of signals between a computer and another peripheral device (for example, a modem) that establishes the parameters required for passing data.

Handshake In

HIN. A general purpose control signal sent from the DTE to DCE in a Newbridge Networks RS-232-C connection. HIN can be used in place of Request to Send (RTS), Carrier Detect (CD) or Ring Indicator (RI).

Handshake Out

HOUT. A general purpose control signal sent from the DCE to the DTE. For example, in the case of a Newbridge Networks Mainstreet Data Controller with ports configured as DCE, HOUT is sent from the Data Controller to an attached device. HOUT can be used in place of Clear to Send (CTS), Carrier Detect (CD) or Ring Indicator (RI).

Handshaking

The initial exchange between two data communications systems prior to and during data transmission to ensure proper data transmission. Handshaking and Line Discipline are the two most basic elements of a communications protocol. A serial (asynchronous) transmission protocol might include the handshake method (XON/XOFF), baud rate, parity setting, number of data bits and number of stop bits. Just as people shake hands, and go through a perfunctory "Hi, how are ya?", computers must go through a procedure of greeting the opposite party, verifying the identity of the other party, determining the maximum speed at which the devices can intercommunicate over a circuit, and other functions that can be described by this "humanizing term." As with human contacts, once the handshaking is complete, the business of communications begins, which is where line discipline comes in. As is always the case, the least capable device determines the specifics of the communication. In other words, the lowest common denominator rules. See also Line Discipline and Protocol.

Handwriting Recognition

A system for taking handwritten text generated with a stylus on a computer pad or directly onto the computer screen, and converting then into machine-readable text.

Hang Up

Hang up lets you disconnect from an ISDN call. To hang up from the phone set you must depress and hold the receiver button for a specified amount of time. By default, the time is set for 0.8 of a second.

Hard Cable

Coaxial cable commonly used in the cable television industry for trunk and feeder. At a minimum, hard cable consists of a copper (or copper -clad aluminum) center conductor, a plastic foam dielectric and a solid-aluminum sheath. The solid aluminum sheath is quite stiff; hence the name. Hard cable is available in several configurations. The most common are:

Bare: There is no protective cover over the aluminum sheath. Bare cable is used in aerial installations where it's lashed to a steel supporting strand; the bare aluminum sheath is readily visible from the ground because of its dull silver color . See Strand .
Jacketed: The sheath is covered with a vinyl jacket, typically black. Jacketed cable is often used in aerial installations located in areas subject to corrosion from industrial pollution or salt; however, many cable companies use jacketed cable in all aerial locations.
Armored: The sheath is covered with three protective layers : a vinyl jacket, a steel wrap, and another vinyl jacket. Armored cable is intended for use in direct- burial applications; the steel armor protects the sheath from damage during installation.
Messengered: Similar to jacketed cable, but includes an integral steel "messenger wire" to provide mechanical support. Messengered cable is intended for aerial installation without strand.

Jacketed and armored cables are also available in "flooded" configurations. Flooded cable contains a sticky, viscous substance called "flooding compound" between the sheath and the jacket. Like a self- sealing tire, flooding compound seals microscopic holes in the jacket to prevent water intrusion. Flooded cables are intended for underground use, but they are not recommended for aerial use (flooding compound is a sticky mess ” literally and politically ” if it drips onto a parked car). Hard cables are identified by "trade size"; i.e., the outside diameter of the sheath. The standard trade sizes are 0.412", 0.500" ("half-inch cable"), 0.625", 0.750", 0.875", and 1.000" ("one inch cable").

Hard Copy

Anything on paper. It is all well and good to have information flash by on your CRT or video display terminal, but there are times when you want to take a Hard Copy with you. This dictionary was written on a computer screen. Now you have a hard copy in your hands. In this case, that's a lot more useful than having a disk.

Hard Decision

See SISO.

Hard Disk Assembly

A sealed mass storage unit used for storing large amounts of data. Now available on personal computers.

Hard Disk Imaging

Today, hard drives are about the only thing that moves constantly on PCs or laptops. As a result, they wear out. i figure it takes me 11 hours from the moment I get a new hard drive to have it running the way I like. The easiest way to repair a busted hard disk is to have a cloned disk, i.e. identical copy of my disk, and pop that hard disk as a replacement for the busted hard disk. When I say "identical" I mean identical. The drive should be the same size and the software on it should be bit-by-bit the same. You produce such a replacement hard disk by using hard disk imaging software. The way it works is typically you turn off your PC, you insert or attach a second hard drive and a insert hard disk imaging or cloning software into your floppy disk drive. You now turn on your PC or laptop. Your machine boots off the floppy. It asks, "Would you like to copy all the material from drive 1 (your main drive) to drive 2 (your backup drive)?" You say Yes and off it goes, copying bit by bit (not file by file) from drive 1 to drive 2. To do this for me takes 35 minutes using a piece of software called EZ-Gig Transfer Utility. How often do I clone my main, working hard disk? Not often enough is my simple answer. The best backup procedure is to clone the disk once a week and back up the data files twice a day ” before lunch and when you're finished for the evening.

Hard Drawn Copper Wire

Copper wire that has been drawn to size and not annealed.

Hard Drive

A sealed hard disk. Originally the hard drive was called the Winchester magnetic storage device. It was pioneered by IBM for use in its 3030 disk system. It was called Winchester because "Winchester" was IBM's code name for the secret research project that led to its invention. A Winchester hard disk drive consists of several "platters" of metal stacked on top of each other. Each of the platter's surfaces is coated with magnetic material and is "read" to and "written" from by "heads" which float across (but don't touch) the surface. The whole system works roughly like the old-style Wurlitzer jukebox. See Winchester.
The Vermonter's Guide to Computer Lingo defines hard drive as getting home during mud season , i.e. it was a hard drive.

Hard Drive Imaging

See Hard Disk Imaging.

Hard Ferrite

Ferrite that remains permanently magnetized. Used to make magnets.

Hard Ground

A direct connection between a device to ground through a wire or other conductor that has a negligible resistance to ground. See also Ground, Grounding (the major explanation), Ground Return and Ground Start.

Hard Handoff

A cellular radio term. A hard handoff is a handoff between cell sites that involves first breaking the connection with the previous cell site before making the connection with the new cell site. A hard handoff, or "break and make" handoff, is not noticeable in a voice conversation, but has disastrous impact on a data communication. Here's a longer explanation: What happens during a Hand-Off Sequence? Hand-off occurs when a call has to be handed from one cell to another as the user moves between cells. In traditional hard hand-off, the connection to the current cell is broken and then the connection to the new cell is made. In CDMA technology, however, it is possible to make the connection to the new cell before leaving the current cell since all cells in CDMA use the same frequency. This is known as a "make-before-break," or "soft hand-off." Soft hand-off requires less power, which reduces interference and increases capacity. See also Handoff.

Hard Plug Loopback

Also known as Hard Loopback. A loopback is a type of diagnostic test in which the transmitted signal is returned to the sending device after passing through a data communications link or network. This allows a technician (or built-in diagnostic circuit) to compare the returned signal with the transmitted signal and get some sense of what's wrong or, more correctly, what's not wrong. Loopbacks are often done by excluding one piece of equipment after another by isolating the equipment from the circuit, or the circuit from the equipment. Loopback tests usually are automated procedures accomplished through a software command which instructs a contact in a CSU/DSU to close a contact in order that the signal "loop back" across the circuit. In effect, this process isolates the equipment from the circuit, allowing the technician or automated test system to speak to the performance of the circuit without any confusion that might be imposed by the equipment, itself. It's a process of elimination . A hard loopback is test that performs the same function on a manual basis, with the technician simply twisting wires together on an RJ-45 or other cable, in order to achieve a hard-wired cross-connection. See also Loopback and Loopback Test.

Hard Problem

A type of calculation which is easy to perform in one direction, but difficult and even impractical to perform in the other direction. In the context of cryptography, hard problems provide extreme levels of security for encrypted data. See also DES and AES.

Hard RAM

Carve some memory out of a computer's RAM; power it continuously and bingo you have Hard RAM, also called a virtual disk. Setting up a RAM disk lets you use your computer's conventional, extended or expanded memory to simulate a disk drive (or drives). The primary advantages of a RAM disk are its very fast access speed and its battery power-saving properties. It has no mechanical element to slow it down or to use additional power.

Hard Rubber

A hard insulating material made of rubber, and having a dielectric constant of from two to four.

Hard Sectoring

Physically marking the sector boundaries of a magnetic disk by punching holes in the disk where there's space available to store data. Hard sectored disks are not very common these days. Most disks ” like those used on the IBM PC ” are soft-sectored.

Hard Tubes

Vacuum tubes having a high vacuum .

Hard Wired

Describes a circuit designed to do one task (e.g. a leased line).
A person with a very narrow and rigid view of his or her job. "That security guard is really hard-wired."

Hardened

Resistant to disaster. Facilities with protective features that have been designed to withstand an explosion, a natural disaster, or ionizing radiation.

Hardware

The actual physical computing machinery, as opposed to software which is the list of instructions to operate the hardware, or the firmware which is combination hardware/software that is "burned into" a Programmable Read Only Memory chip or chips. See Firmware and Software.

Hardware Address

Also called physical address or MAC-layer address, a data-link layer address associated with a particular network device. Contrasts with network or protocol address, which is a network layer address.

Hardware Flow Control

Hardware flow control is the method used by the UART chip (that chip controls the serial port) to modulate the flow of data. It does this by controlling the Clear to Send/Ready to Send (CTS/RTS) lines of the serial port's interface. For example, it can turn off or re-enable the flow of data. Most high-speed sessions require hardware flow control due to their need for precise, instantaneous control over the flow of incoming and outgoing data.

Hardware Interrupt

See Interrupt.

Hardware Tree

A Windows 95 term. A record in RAM of the current system configuration information for all devices in the hardware branch of the Registry. The hardware tree is created each time the computer is started or whenever a dynamic change occurs to the system configuration.